Diabetes mellitus, often simply referred to as diabetes, is a significant global health concern and is a leading cause of illness and death. This is true even in developed countries, where elevated weight and obesity contributes to certain forms of diabetes. Although various methods of controlling diabetes and its symptoms have been found, there is yet no cure.
Insulin is a hormone produced in the pancreas and is used by the body to convert sugar and other foods into energy. Individuals affected with diabetes either do not produce sufficient insulin or do not respond properly to the insulin they produce. Sugar levels in the body therefore build until the sugar is excreted through urine. Those afflicted with diabetes suffer from various ailments, including ailments affecting the eyes, kidneys, heart, and limbs.
Persons with Type 1 diabetes generally do not produce insulin and represent approximately 5-15% of all cases. Type 1 diabetes was formerly referred to as juvenile-onset diabetes or insulin-dependent diabetes mellitus (IDDM) and almost always requires the person afflicted to take insulin injections. Type 2 diabetes, formerly referred to as adult-onset diabetes or non-insulin-dependent diabetes mellitus (NIDDM), represents the remaining 85-95% of cases and is usually associated with persons over the age of 40. Type 2 diabetes develops slowly as one ages, typically in association with obesity or unhealthy weight gain.
Since the early 1920's, all forms of diabetes have been treatable with insulin. Insulin allows persons with diabetes to live nearly normal lives with virtually no long term affects if administered properly. For those with Type 1 diabetes who have limited or no natural insulin production, therapies typically include routine insulin injections. Those with Type 2 diabetes are typically treated through diet control, weight loss, and exercise, although insulin injections may also be required occasionally.
Individuals with Type 2 diabetes that control their blood-sugar level through diet may test their blood sugar level once per day, generally before breakfast. Persons with Type 1 diabetes and Type 2 diabetes that utilize insulin injections may test more often, typically at least 3 times and as often as times per day. Such testing means typically include piercing of the skin and placing a droplet of blood on a test strip. The test strip may in turn change color to represent a blood-glucose level, or may be associated with a meter that provides a digital representation of the blood-glucose level. In any event, only at the moment of testing does one know their blood glucose level.
Many believe that the future of glucose testing lies in methods that enable continuous blood glucose monitoring (CGM) so as to avoid the need for testing by the patient and to provide a greater level of accuracy in testing, at least by virtue of additional data points. A typical CGM consists of a disposable glucose sensor placed under the skin, a receiver that a user may wear on his/her body much like a pager, and a transmitter adapted to provide communication between the sensor and the meter. Although there are few currently available commercial systems, those that are available typically have sensors that last between 3 and 7 days in vivo. As such, the sensors must be replaced periodically.
CGM sensors typically include a polymer membrane that may be damaged or otherwise compromised during insertion. Yet, it is presently difficult to assess sensor viability after insertion. Even if not damaged during insertion, the membrane may incur biofouling through biological reaction within the body, such as through protein absorption, which adversely affects performance of the sensor.
Another issue with sensors that is difficult to currently assess is the level of movement of the sensor once inserted. Such movement is typically referred to as pistoning, and is preferably avoided for most accurate readings as the movement causes inconsistent readings.
It would therefore be advantageous to provide a sensor system and method for determining the viability of a sensor in vivo. It would be most preferred if a calibration profile of the sensor could be adjusted in response to changing conditions in vivo.